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  • Land Surveyor
    Ravi Shankar July 15, 2018 at 1:57am

    Question for the experts:

    During Railway alignment and topographical survey for 260km long rail corridor , I came across a process where a survey company followed the below procedure


    1. Established DGPS Stations every 5 km using whole to part concept. Total of 85 control point pairs have been established in 260km long corridor.

    2. Converted the  DGPS control points coordinates to grid coordinates - UTM 44 N


    3. Again converted the UTM Coordinates to modified UTM ("they are calling it Plane UTM"). 
    Few of the coordinates are given below
    1. GPS83 22° 24' 11.03540" N 82° 27' 58.76349" E UTM Coord: Easting 650935.447 Northing 2478177.945 0.000 0.000 Modified UTM : E-650935.447 N- 2478177.945
    2. GPS83A 22° 24' 09.69999" N 82° 27' 59.28814" E UTM: Easting -650950.851, Northing-2478137.021 -0.002 0.004 Modified UTM: Easting-650950.853, Northing-2478137.017
    3. GPS84 22° 24' 53.94240" N 82° 29' 24.71701" E UTM: Easting -653380.418, Northing-2479521.729 -0.276 -0.158 Modified UTM: Easting -653380.694, Northing- 2479521.887
    4. GPS85 22° 25' 21.78230" N 82° 31' 25.31431" E UTM: Easting -656820.2538 Northing-2480412.551 -0.633 -0.241 Modified UTM: Easting -656820.8864 Northing-2480412.792


    Is the term "Plane UTM" a standard term used by surveyors?For Plane UTM coordinates the UTM standard projection parameters have been tweaked;


    Modified Projection Details

    1 Ellipsoid WGS-84

    2 Semi-major axis 6378137

    3 Flattening-1/f 298.2570

    4 Projection Plane UTM

    5 False Easting 650935.447

    6 False Northing 2478177.945

    7 Latitude of Origin 22° 24' 11.03540" N

    8 Central Meridian 82° 27' 58.76349" E

    9 Scale factor at Origin 1.0000

    10 Average Projection Scale Factor 1.00001583749

    11 Average Elevation Factor 0.99996171802

    12 Average Combined Factor 0.99997755494


    My question is tweaking the False Easting and Flase Northing (the values belong to first DGPS Control point), a standard practice?


    The project is a linear 260 km running in the direction: North East to South West.
    The entire project corridor is inside UTM zone 44 N.


    4. The entire control point traverse survey and detailed topographical survey was carried using Total station using Plane UTM coordinates


    5. The railway alignment design was done in AutoCAD using the plane UTM coordinates.


    6. The survey company didn't re-convert the plane UTM topo features coordinates and plane UTM based railway corridor coordinates (Centerline, Right and left corridor points) back to standard UTM coordinates,which was a matter of concern for me?

    The survey company created KML of the designed corridor using the plane UTM coordinates , which obviously didn't show the correct location or match the google earth


    Any thoughts and suggestions?


    Thanks

  • Survey Legend
    ⚡Survenator⌁ July 3, 2018 at 8:33pm

    Thank you for sharing Erwin!   Care to tell us anymore about the project?

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